Small portable electronic devices that are capable of storing relatively large amounts of data (e.g. hundreds of megabytes or several gigabytes, sometimes tens of gigabytes) and that can be easily connected to and disconnected from computers are becoming ever more popular as they provide a convenient way for users to transport computer data. In many cases such devices can be easily connected to a host computer by means of plug-and-play technology and present themselves to the host computer's operating system as a mass storage device (MSD) with a standard file system. In many cases the interface to connect the device to the host computer is of the USB (Universal Serial Bus) type. So called USB keys or USB memory sticks are examples of such devices. In some cases the device offers other functionality or the mass storage functionality is integrated into a device with another main functionality. For example, some USB keys also contain a smart card or smart card chip and offer security functions (often in the context of a Public Key Infrastructure (PKI)), while many digital cameras can be connected to a computer via a USB connection and are then visible to the host computer as a mass storage device.
Because they are so convenient for transporting computer data, these portable mass storage devices are often used to store and transport confidential or otherwise sensitive data. As such they may represent a security risk that is exacerbated by their relatively small size, which makes them prone to theft or loss.